Split-gate semiconductor devices typically include a number of gates that are insulated from one another by inter-gate dielectric structures. FIG. 2A illustrates one embodiment of split-gate semiconductor device 200 formed on a substrate 202. Semiconductor device 200 includes a first gate 210 disposed over a gate dielectric structure 214, a second gate 208 disposed over a gate dielectric structure 212, and a single-layer inter-gate dielectric structure 216 disposed between the two gates. The integrate dielectric structure 216 may be made of, but is not limited to, silicon dioxide. FIG. 2B illustrates the same semiconductor device 200 after it has gone through further wet etch or wet clean stages during the fabrication process. In this case, the inter-gate dielectric structure 216 is shown with a portion removed at region 218, creating a gap between gate 208 and gate 210. In subsequent stages of fabrication, this gap may get filled with a lower quality dielectric 220, as shown in FIG. 2C, or undesired chemical residues, or may even form voids. Consequently, the electrical isolation between the two gates may be weakened, leading to excessive leakage current and possibly an early dielectric breakdown between the two gates.
FIGS. 3A-3C illustrate another embodiment of split-gate semiconductor device 300, that is similar to semiconductor device 200 depicted in FIGS. 2A-2C. In one embodiment, the inter-gate dielectric structure 316 may include up to three layers of different dielectric films, such as silicon dioxide/silicon nitride/silicon dioxide. FIG. 3B depicts portions of the inter-gate dielectric structure removed after the semiconductor device depicted in FIG. 3A has gone through further wet etch or wet clean stages during the fabrication process. In FIG. 3B, the dielectric films of the inter-gate dielectric structure are shown to be removed in an uneven manner because etch rates vary based on the wet chemicals used to etch the specific dielectrics. Once again, the gap created between gate 308 and gate 310 may get filled with a lower quality dielectric 320, as shown in FIG. 3C. Undesired chemical residues or even voids may result, weakening the electrical isolation between the two gates. Such undesirable consequences may lead to excessive leakage current and possibly an early dielectric breakdown between the two gates.
What may be needed are split-gate semiconductor devices and methods for manufacturing them that result in inter-gate structures that may not suffer from the above shortcomings.